Mechanisms having two articulately interconnected rotatable components are well known in the art. The articulated or pivotal connection between the rotatable components allows for flexural movement of the components relative to each other while maintaining a rotatable drive connection therebetween. For example, a constant velocity joint on a vehicle is comprised of two pivotally interconnected and elongated members which operate to transfer rotary motion and torque. The pivotal joint allows the members to flexibly and angularly move out of axially aligned relation relative to each other while maintaining the capability of transferring rotary motion therebetween with little or no loss of power.
As will be appreciated by those skilled in the art, and during operation of the joint, the relative movement between the components comprising the pivot or articulate connection between the members can give rise to significant friction forces especially when the elongated members are flexibly or angularly disposed relative to each other. Accordingly, it is c ,mm.sub.1 n to lubricate the component parts of the constant velocity joint in an effort to reduce the fiction forces. Different forms of grease or other suitable lubricants have been used to effect ends.
Depending upon the environment in which tile constant velocity joint is disposed, the components of the joint are commonly subjected to dust, dirt and other contaminants Unfortunately, the grease or lubricant used to reduce the frictional forces between the components of the mechanism tends to attract and intermix with the contaminants, thus, adversely affecting the interrelationship between the component parts of the constant velocity joint. This problem is exacerbated when the constant velocity joint is arranged on a vehicle. As the vehicle is driven across a field or road, the wheels or tires tend to pick up dirt, stones, moisture, and etc. As is well known, a constant velocity joint of a vehicle is typically arranged in an area disposed proximate to the wheel of the vehicle and, thus, is subject to the dust; dirts moisture, stones and other contaminants directed there toward with forceful movement by the wheels or tires of the vehicle. As mentioned, the lubricant conventionally used in combination with the constant velocity joint of the vehicle typically mixes with the contaminants, thus, adding the problem of wear between the components of the constant velocity joint.
To inhibit contaminants from interfering with the constant velocity joint, seals or boots for protectively covering the joint have been proposed. One of the more common seals or boots that have been designed to protect constant velocity joints has a bellowed configuration between opposite ends thereof. That is, series of joined and adjacent bellow-like configurations art disposed between opposite ends of the seal. Each bellow-like configuration of the seal includes crest and root diameters with annularly and angularly diverging wall sections extending therebetween.
Such seals or boots envelope the constant velocity joint and allow the pivotally interconnecting drive components to axially extend outwardly from opposite ends thereof while the bellow-like configurations provide the flexibility required to allow the interconnected drive components to angularly and linearly move relative to each other. As will be appreciated, during operation of the constant velocity joint, the bellows portion of the seal is subject to substantial flexural forces as the seal is required to continually expand, retract, turn and angulate. Because of the severe flexural forces imparted to the bellow seal or boot during operation of the constant velocity joint, such seals tend to fail quickly.
Manufacturing costs associated with a vehicle are an important concern. Each vehicle typically includes at least two bellow seals or boots for protecting an equal number of constant velocity joints. Some vehicles require four or more bellow seals for protecting the constant velocity joints thereon. Accordingly, it is imperative that the cost of the seals or boots be minimized.
Constant velocity joint seals made of silicon advantageously retain their flexibility but are generally relatively expensive. Constant velocity joint seals or boots manufactured from natural rubber products have poor durability during operation and tend to quickly fail thus exposing the constant velocity joint protected thereby to contaminants. In the vast majority of applications, a bellowed seal is manufactured using blow molding techniques. Often steel reinforcing rings are placed around the bellow seal to give it radial strength.
While bellowed seals or boots manufactured using blow molding techniques offer certain advantages over silicon or rubber bellowed seals, they have certain limitations of their own which often prove to be a significant disadvantage when used in combination with twisting and turning constant velocity joints. For one thing, the material thicknesses of injection blow molded seals is difficult to control with regularity du ring their manufacturing process. Accordingly, the annular and angularly diverging walled sections of each bellow-like configuration typically varies in material thickness about their circumference and the material thicknesses of the wall sections of the bellow-like configurations often noncontrollably vary even between adjacent bellow-like configurations. Moreover, it is difficult to control the material thicknesses of the root and crest diameter sections of each bellow-like configuration when the seal is formed using blow-molding grade materials and blow molding techniques.
During an injection blow molding manufacturing process for bellowed seals, an elongated, molten, cylindrical-like parison of blow-nmolded thermoplastic material having about a 1.8 to 2 melt-flow rate value at the 230.degree. C. and under 2160 g. load is introduced into a die assembly. After introducing the parison into the mold, the elongated and molten parison is blown outwardly under pressure to foni the relatively deep bellows typically inherent with constant velocity joint seal or boot designs. As mentioned, however, blow molding techniques used to form bellowed seals from molten parisons typically result in considerable variances in the material thicknesses in different areas along the length and about the bellowed seal. These variations in material thicknesses about the annular wall sections, as well material thicknesses at the root and crest diameters of the bellows, along the length of and about the circumference of the seal, resulting from known manufacturing processes cause difficulty in controlling material thicknesses, tend to result in different load stresses being imparted toward to the seal or boot as it expands, retracts, flexes, turns and angulates during its flexural operation.
Constant velocity joints protected by the bellowed seals are not visually apparent on most vehicles. To the contrary, the bellowed seals are usually disposed in areas usually visible only if and when the vehicle is elevated. Since the purpose of the seal is to prevent contaminants from interfering with proper operation of the constant velocity joint, failure of seal is likewise substantially undetectable. Accordingly, a substantial time period can elapse between the time when the bellowed seal initially fails to completely protect the constant velocity joint and the time such failure is detected. In the interim, substantial irreparable damage can occur to the constant velocity joint.
Thus, there continues to be a need and a desire for a constant velocity joint seal that is economical to manufacture, that offers increased durability from heretofore known injection blow-molded seals, and which can be manufactured using simplified processes.